Internet protocol multimedia subsystems (IMS) integrate networks such as public switched telephone networks (PSTN) and mobile communication networks so as to provide users (or subscribers) with various communication services, wherein the IMS serving as a pivotal role in the next generation network (NGN) is standardized by the third generation partnership project (3GPP).
Electronic mailing services have suffered from social problems such as Spam and unsolicited (or junk) mails, which are unwanted mails unilaterally sent to recipients by senders. Unsolicited communications occur due to various factors derived from the popularization of the Internet, such as significant decreases of communication costs and advanced capabilities of network access terminals (such as personal computers purchasable by common users) transmitting numerous electronic mails to unspecified persons or sites.
The above problem (already occurring in electronic mailing services) seems to occur in the IMS due to its popularization. The 3GPP specification has initiated the protection against unsolicited communication for IMS (simply referred to as “PUCE”) to protect users from Spam over the IP telephony (SPIT).